Syntheses, structures, and properties of some piano-stool iron acetylides bearing a functional anthracenyl group

Article abstract of DOI:10.1021/om701278e

The present study reports the isolation and the structural (X-ray), electrochemical (CV), and spectroscopic (IR, Moessbauer, ESR, UV-vis-NIR) characterization of the new complexes [(η²-dppe) (η⁵-C₅Me₅)Fe(-C≡C-9,10-ant-X)] ⁿ⁺ n[Y] (dppe = 1,2-bis(diphenylphosphino)ethane; ant = anthracene; n = 0, 1; 3aⁿY, X = H; 3bⁿY, X = Br; 3cⁿY, X = CN; 3d, X = C≡C-SiⁱPr₃; 3e, X = C≡C-H; Y = PF₆, TCNE, TCNQ). It was shown that anthracene acts as a better transmitter than phenyl. The electron density on the Fe(III) nucleus depends on the distance between the metal center and the counteranion. The bulky (η²-dppe)(η⁵-C₅Me₅)Fe moiety is big enough to push the anthracene rings further apart and disrupts π-π stacking except in the case of 3c[TCNE] for which stacking is observed both between the TCNE anion and the (C₅Me₅) ligand and between anthracene fragments. The Fe(II) complexes display MLCT transitions in the 550-650 nm range while LMCT transitions can be observed in the 600-850 nm spectral range for the Fe(III) complexes. The Fe(II) and Fe(III) complexes exhibit weak luminescence property derived from the alkynyl anthracene units. Both Fe(II) and Fe(III) moieties can quench the ligand-centered emission by two different mechanisms.

Full text of DOI:10.1021/om701278e

1912
Organometallics 2008, 27, 1912–1923
Syntheses, Structures, and Properties of Some Piano-Stool Iron
Acetylides Bearing a Functional Anthracenyl Group
Frédéric de Montigny,†,‡ Gilles Argouarch,† Thierry Roisnel,† Loic Toupet,†
Claude Lapinte,†,* Sally Chan-Fung Lam,§ Chi-Hang Tao,§ and Vivian Wing-Wah Yam§,*
Sciences Chimiques de Rennes, UMR CNRS 6226, UniVersité de Rennes 1, 35042 Rennes, France, Groupe
Matière Condensée et Matériaux, UMR CNRS 6626, UniVersité de Rennes 1, 35042 Rennes, France, and
Centre for Carbon-Rich Molecular and Nano-Scale Metal-Based Materials Research and Department of
Chemistry, The UniVersity of Hong Kong, Pokfulam Road, Hong Kong, People’s Republic of China
ReceiVed December 21, 2007
The present study reports the isolation and the structural (X-ray), electrochemical (CV), and spectroscopic
(IR, Mössbauer, ESR, UV–vis-NIR) characterization of the new complexes [(η2-dppe)(η5-C5Me5)Fe(-CtC-
9,10-ant-X)]n+n[Y] (dppe ) 1,2-bis(diphenylphosphino)ethane; ant ) anthracene; n ) 0, 1; 3anY, X )
H; 3bnY, X ) Br; 3cnY, X ) CN; 3d, X ) CtCsSiiPr3; 3e, X ) CtCsH; Y ) PF6, TCNE, TCNQ).
It was shown that anthracene acts as a better transmitter than phenyl. The electron density on the Fe(III)
nucleus depends on the distance between the metal center and the counteranion. The bulky (η2-dppe)(η5-
C5Me5)Fe moiety is big enough to push the anthracene rings further apart and disrupts π-π stacking
except in the case of 3c[TCNE] for which stacking is observed both between the TCNE anion and the
(C5Me5) ligand and between anthracene fragments. The Fe(II) complexes display MLCT transitions in
the 550–650 nm range while LMCT transitions can be observed in the 600–850 nm spectral range for
the Fe(III) complexes. The Fe(II) and Fe(III) complexes exhibit weak luminescence property derived
from the alkynyl anthracene units. Both Fe(II) and Fe(III) moieties can quench the ligand-centered emission
by two different mechanisms.
Mononuclear organometallic acetylide complexes featuring one
or several unpaired electrons exhibit usually a very rich chemistry
and constitute a tremendous potential for molecular electronics,
since redox-active organometallics stable under several oxidation
states can be envisioned either as electron reservoirs or spin
carriers.18–20 This is particularly true for species containing the (η2-
dppe)(η5-C5Me5)Fe(CtC)- fragment,21–28 owing to the potential
these compounds offer for redox switching when incorporated in
Introduction
Considerable interest is now focused on the development of
multifunctional molecular systems with synergetic properties.1–4
In particular, assemblages incorporating redox and/or photoac-
tive groups as a donor and/or acceptor have been the subjects
of considerable recent research, as their attractive electronic and
physical properties make them suitable candidates for switchable
5–8
optical materials,
electrode surface modifiers,9,10 and mag-
netic materials.11–17
(13) Nakanishi, S.; Ojima, T.; Akutsu, H.; Yamada, J.-I. J. Org. Chem.
2002, 67, 916–921.
(14) Takeuchi, S.; Ogawa, Y.; Naito, A.; Sudo, K.; Yasuoka, N.; Akutsu,
H.; Yamada, J.-I.; Nakatsuji, S. Mol. Cryst. Liq. Cryst. 2000, 345, 167.
(15) Nakatsuji, S.; Ogawa, Y.; Takeuchi, S.; Akutsu, H.; Yamada, J.-I.;
Naito, A.; Sudo, K.; Yasuoka, N. J. Chem. Soc., Perkin Trans. 2000, 2,
1969.
(16) Nakatsuji, S.; Takahashi, S.; Ojima, T.; Ogawa, Y.; Akutsu, H.;
Yamada, J.-I. J. Mol. Cryst. Liq. Cryst. 2001, 356, 23.
(17) Miller, J. S.; Epstein, A. J. Angew. Chem., Int. Ed. Engl. 1994, 33,
385–415.
* To whom correspondence should be addressed. E-mail: lapinte@
univ-rennes1.fr; wwyam@hku.hk.
† University of Rennes 1.
‡ Present address: ENSCP-UMR7576, 11 rue Pierre et Marie Curie
75231, Paris Cedex 05, France.
§ The University of Hong Kong.
(1) Marder, S. R. Inorganic Materials, 2nd ed.; Wiley: Chichester, UK,
1996.
(2) Long, N. J. Angew. Chem., Int. Ed. 1995, 34, 21–38.
(3) Hudson, R. D. A. J. Organomet. Chem. 2001, 637–639, 47.
(4) Paul, F.; Lapinte, C. Coord. Chem. ReV. 1998, 178–180, 427–505.
(5) Samoc, M.; Gauthier, N.; Cifuentes, M. P.; Paul, F.; Lapinte, C.;
Humphrey, M. G. Angew. Chem. 2007, 45, 7376–7379.
(6) Cifuentes, M. P.; Humphrey, M. G.; Morrall, J. P.; Samoc, M.; Paul,
F.; Lapinte, C.; Roisnel, T. Organometallics 2005, 24, 4280–4288.
(7) Weyland, T.; Ledoux, I.; Brasselet, S.; Zyss, J.; Lapinte, C.
Organometallics 2000, 19, 5235.
(18) Venkatesan, K.; Blacque, O.; Fox, T.; Alfonso, M.; Schmalle, H.;
Kheradmandan, S.; Berke, H. Organometallics 2005, 24, 920–932.
(19) Astruc, D. Electron Transfer and Radical Processes in Transition-
Metal Chemistry; VCH: New York, 1995; p 630.
(20) Kahn, O. Molecular Magnetism; VCH Publishers, Inc.: New York,
1993; p 380.
(21) Le Narvor, N.; Toupet, L.; Lapinte, C. J. Am. Chem. Soc. 1995,
117, 7129–7138.
(22) Le Narvor, N.; Lapinte, C. Organometallics 1995, 14, 634–639.
(23) Weyland, T. Synthèse et Propriétés de Complexes Organo-fer Bi-
et Tri-nucléaires sous differents degrés d’oxydation. Ph.D. Thesis, Rennes
1, Rennes, 1997.
(8) Wong, K. M.-C.; Lam, S. C.-F.; Ko, C.-C.; Zhu, N.; Yam, V.
W.-W.; Roué, S.; Lapinte, C.; Fathallah, S.; Costuas, K.; Kahlal, S.; Halet,
J.-F. Inorg. Chem. 2003, 42, 7086–7097.
(9) Armstrong, N. R.; Carter, C.; Donley, C.; Simmonds, A.; Lee, P.;
Brumbach, M.; Kippelen, B.; Domercq, B.; Yoo, S. Thin Solid Films 2003,
445, 342.
(24) Weyland, T.; Costuas, K.; Mari, A.; Halet, J.-F.; Lapinte, C.
Organometallics 1998, 17, 5569–5579.
(25) Weyland, T.; Costuas, K.; Toupet, L.; Halet, J.-F.; Lapinte, C.
Organometallics 2000, 19, 4228–4239.
(10) Zou, C.; Wrighton, M. S. J. Am. Chem. Soc. 1990, 112, 7578.
(11) Sato, O.; Iyoda, T.; Fujishima, A.; Hashimoto, K. Sciences 1996,
272, 704.
(26) Denis, R.; Toupet, L.; Paul, F.; Lapinte, C. Organometallics 2000,
19, 4240–4251.
(12) Nagai, K.; Iyoda, T.; Fujishima, A.; Hashimoto, K. Solid State
Commun. 1997, 102, 809.
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10.1021/om701278e CCC: $40.75
2008 American Chemical Society
Publication on Web 03/15/2008

Piano-Stool Iron Acetylides
Organometallics, Vol. 27, No. 8, 2008 1913
mediated through anthracene units.35 The strong fluorescence
of anthracenes constitutes also key properties for designing novel
chemosensors and multifunctional materials.36–38 The properties
of anthracene derivatives to adsorb onto the side walls of single-
walled carbon nanotubes (SWNTs) might open a route toward
functional nanoparticles and supramolecular assemblies.39 In a
previous work we reported that the 9,10-bis(ethynyl)anthracene
bridge mediates electron transfer and electron exchange between
[(η2-dppe)(η5- C5Me5)Fe]n+ (n ) 0, 1) building blocks (2, Chart
1). Taken as a whole, the experimental and theoretical data
emphasized the specific role of the anthracene fragment, which
allows good communication between the remote iron centers
and favors the displacement of the spin density from the metal
centers onto the R and ꢀ sp carbon atoms in the vicinity of the
metal and the ipso carbon of the anthracene.40
Chart 1
In the course of our research to develop novel organometal-
lics, we report here the synthesis of the neutral and radical cation
complexes [(η2-dppe)(η5- C5Me5)Fe(-CtC-9,10-ant-X)]n+n[Y]
(ant ) anthracene; n ) 0, 1; 3anY, X ) H; 3bnY, X ) Br;
3cnY, X ) CN; 3d, X ) CtCsSiiPr3; 3e, X ) CtCsH; Y )
PF6-, TCNE-, TCNQ-). An extensive analysis of the properties
of this new family of molecules including redox potentials,
X-ray determination, and Mössbauer, vibrational, and electronic
spectroscopies was achieved and the data were compared with
those obtained for the mononuclear complexes [(η2-dppe)(η5-
C5Me5)Fe(CtCsC6H4X)]n+n[Y]. It was envisaged that the
luminescence properties of the anthracenyl group would be
perturbed, varied, or tuned by the electroswitchable iron(II)/
iron(III) building block and the luminescent properties of
3an[PF6] and 3cn[PF6] (n ) 0, 1) were studied and compared.
molecular devices.4,29 In several instances, we have shown that
this remarkable fragment allows efficient switching of various
electronic properties of the complexes, such as ferromagnetic
interactions,24,25 fluorescence,8 and nonlinear optical hyperpolari-
zability.5,30,31 This effect results from the change in redox state of
the iron center that is “transmitted” to the rest of the molecule
through the alkynyl spacer. Mononuclear Fe(II)/Fe(III) compounds
such as [(η2-dppe)(η5-C5Me5)Fe(CtCsC6H4X)]n+n[Y] have been
extensively studied by some of us as model complexes to
understand the influence of the substituents on the bonding
properties within the metal-acetylide backbone (1, Chart 1).28,32,33
To introduce new functionalities in these complexes we have
linked an anthracenyl moiety onto an iron alkynyl building block
to generate the new series of complexes [(η2-dppe)(η5-
C5Me5)Fe(CtC-9,10-C14H8X)]n+n[Y]. Indeed, substituted an-
thracenes which possess a wide range of chemical and physical
properties constitute very attractive building blocks for the
construction of new multifunctional molecular devices with
optical and magnetic properties. In particular, these compounds
are known to dimerize upon irradiation in solution and/or in
the solid state and the chromophoric system is therefore a
promising system for investigating the change of magnetic
properties in a spin system by their structural change upon
irradiation.34 On the other hand, it has been shown that very
strong ferromagnetic coupling between organic radicals can be
Results
1. Synthesis of the Neutral Complexes 3a-e. The substi-
tuted Fe(II) σ-acetylide complexes 1 were essentially prepared
by a Pd/Cu-catalyzed cross-coupling reaction between the iron
acetylide (η2-dppe)(η5-C5Me5)FeCtCH (8) and the correspond-
ing substituted aryl bromide.26 However, with the electron-rich
(η2-dppe)(η5-C5Me5)Fe building block and a functional an-
thracene moiety the cornerstone of this chemistry rests in the
recovery of the target products in a pure form. Indeed,
chromatographic purification of the Fe(II) complexes proved
detrimental in many cases and the presence of an anthracenyl
group often limits the solubility of the material.
The optimization of the syntheses constitutes a prerequisite to
limit the presence of side products at the lower level. For this reason
we have compared the efficiency of the two possible routes to
access to the complexes 3a-d. The classical vinylidene route
depicted in Scheme 1 (route A) can be carried out in the one-pot
procedure by using trimethylsilylalkynylanthracene derivatives
4a-d and the iron chloride 6. Alternatively, the “metalla-
Sonogashira” coupling reaction between the iron acetylide 8 and
the haloanthracenes 5a-d and 9 (route B) can be envisioned as a
(28) Paul, F.; Toupet, L.; Thépot, J.-Y.; Costuas, K.; Halet, J.-F.; Lapinte,
C. Organometallics 2005, 24, 5464–5478.
(29) Paul, F.; Lapinte, C. Magnetic communication in binuclear orga-
nometallic complexes mediated by carbon-rich bridges. In Unusual
Structures and Physical Properties in Organometallic Chemistry; Gielen,
M., Willem, R., Wrackmeyer, B., Eds.; John Wiley & Sons: London, UK,
2002; pp 220–291.
(35) Kaneko, T.; Makino, T.; Miyaji, H.; Teraguchi, M.; Aoki, T.;
Miyasaka, M.; Nishide, H. J. Am. Chem. Soc. 2003, 125, 3554–3557.
(36) Witulski, B.; Weber, M.; Bergsträsser, U.; Desvergne, J.-P.; Bassani,
D. M.; Bouas-Laurent, H. Org. Lett. 2001, 3, 1467–1470.
(37) Carano, M.; Cicogna, F.; D’Ambra, I.; Gaddi, B.; Ingrosso, G.;
Marcaccio, M.; Paolucci, D.; Pinzino, C.; Roffia, S. Organometallics 2002,
21, 5583.
(30) Weyland, T.; Ledoux, I.; Brasselet, S.; Zyss, J.; Lapinte, C.
Organometallics 2000, 19, 5235–5237.
(31) Paul, F.; Costuas, K.; Ledoux, I.; Deveau, S.; Zyss, J.; Halet, J.-F.;
Lapinte, C. Organometallics 2002, 21, 5229–5235.
(32) Costuas, K.; Paul, F.; Toupet, L.; Halet, J.-F.; Lapinte, C.
Organometallics 2004, 23, 2053–2068.
(38) Cicogna, F.; Colonna, M.; Houben, J. L.; Ingrosso, G.; Marchetti,
F. J. Organomet. Chem. 2000, 593–594, 251–266.
(33) Paul, F.; da Costa, G.; Bondon, A.; Gauthier, N.; Sinbandhit, S.;
Toupet, L.; Costuas, K.; Halet, J.-F.; Lapinte, C. Organometallics 2007,
26, 874–896.
(39) Zhang, J.; Lee, J.-K.; Wu, Y.; Murray, R. W. Nano Lett. 2003, 3,
403–407.
(34) Bouas-Laurent, H.; Castellan, A.; Desvergne, J.-P.; Lapouyade, R.
Chem. Soc. ReV. 2000, 29, 43.
(40) de Montigny, F.; Argouarch, G.; Costuas, K.; Halet, J.-F.; Roisnel,
T.; Toupet, L.; Lapinte, C. Organometallics 2005, 24, 4558–4572.

1914 Organometallics, Vol. 27, No. 8, 2008
de Montigny et al.
Scheme 1a
t
i
a
Key reagents: (i) CH3OH, K2CO3, NaBPh4, 20 °C, 16 h; (ii) CH3OH, KOBu , 20 °C, 4 h; (iii) HN( Pr)2, THF, PdCl2(PPh3)2, CuI, 20–70 °C,
10 h.
Scheme 2a
a
Key reagents: (i) THF, TBAF, 50 °C, 16 h.
second pathway.41 The organic anthracene-containing molecules
were previously prepared and their syntheses separately reported.42
Route A provides the complexes 3a and 3b in good yields, but
the samples were always contaminated by a small amount of the
corresponding terminal alkynes and their purification remained
unsuccessful. This route is not suitable in the case of complex 3c,
the coordination of the nitrile being probably faster than the alkyne
activation. However, complex 3d was advantageously prepared by
reaction of 6 with 9-triisopropylsilylethynyl-10-ethynylanthracene
obtained from 4d and isolated as a dark red powder in 57% yield.42
The alternative route B did not allow the isolation of 3a,b as pure
samples, when 8 was reacted with 5a,b in presence of the Pd/Cu
catalysts. However, the more reactive iodide 9 provided 3a in a
pure form after washing with pentane (71%). The same route
allowed the easy preparation of 3c with a good yield (83%). In
the case of complex 3b, the oxidation with [(η5-C5H5)2Fe][PF6]
of the contaminated material obtained by either route A or B gave
3b[PF6] as a pure brown powder in 43–45% yield. The reversible
reduction of 3b[PF6] with KOBut provides pure 3b in 87% yield.
Treatment of 3d with TBAF in THF cleanly afforded complex 3e
as a pure red powder (82%, Scheme 2).
structures (Figure 1). Satisfactory HRMS and/or elemental
analyses were also obtained for most of these new compounds.
All complexes were spectroscopically pure, as exemplified by
the observation of a single 31P NMR peak for the dppe ligand
and a clean and sharp 1H NMR signal for the methyl resonance
of the C5 ring. The low solubility of all these complexes
precluded recording 13C NMR spectra. The NMR data are in
line with the usual features expected for complexes of the (η2-
dppe)(η5-C5Me5)Fe series. The 31P NMR shift spans a very
narrow range between δ 100.8 and 101.8 and the 1H NMR shift
of (η5-C5Me5) remains between δ 1.55 and 1.68.
The complexes were also characterized by a typical infrared
absorption at 1986–2022 cm-1, which corresponds to the
vibration mode of the CtC bond coordinated to the iron center
(Table 1). Another vibration mode was also observed at higher
energy (2111–2118 cm-1) for the complexes 3d and 3e and
attributed to the noncoordinated CtCsSiiPr3 and CtCsH
bonds. In a previous work on Fe(II) acetylides (η2-dppe)(η5-
C5Me5)Fe(CtCsC6H4sX) (1), we observed that the stretching
frequency for the triple bond (νC≡C) was dependent on the
electronic nature of the appended substituent X and its evolution
could be quantitatively rationalized by using a valence bond
formalism, considering that electron-withdrawing substituents
in Fe(II) acetylides favor the cumulenic character of the alkynyl
bridge. Comparison of the previous results26 with those obtained
for the anthracene-containing series 3 indicates that the an-
thracene enhances the cumulenic character and increases the
sensitivity to the electronic properties of X (Scheme 3). Indeed,
the νC≡C frequencies decrease as the phenyl group is replaced
2. Characterization of the Neutral Complexes 3a-e. The
neutral complexes were characterized by the usual spec-
troscopies and high-resolution LSI mass spectrometry, while
X-ray data obtained for 3b and 3c confirmed the proposed
(41) Suzuki, H.; Kondo, A.; Inouye, M.; Ogawa, T. Synthesis 1986, 1,
121–122.
(42) de Montigny, F.; Argouarch, G.; Lapinte, C. Synthesis 2006, 293–
298.

Piano-Stool Iron Acetylides
Organometallics, Vol. 27, No. 8, 2008 1915
Figure 1. Drawings of 3b (A), 3c (B), 3c[PF6] (C), 3c[TCNE] (D), and 3c[TCNQ] (E) with selected atomic numbering. Thermal ellipsoids
represented at the 50% probability level. Hydrogen atoms and solvent molecules are omitted for clarity.
by the anthracenyl fragment and the amplitude of the effect
(∆νC≡C) increases with the electron-withdrawing character of
the X group from 31, 52, and 61 cm-1 for X ) H, Br, and CN,
respectively.
well-known metal-centered Fe(II)/Fe(III) oxidation, and as
expected it indicates that the Fe(III) analogues are stable at the
platinum electrode. They constitute accessible synthetic targets.
It is apparent that the presence of an electron-withdrawing
substituent on the anthracene fragment makes the oxidation of
the metal center more difficult, and for the same substituent
this effect is larger than in the related series 1. These results
corroborate the IR data.
3. Synthesis and Characterization of the Oxidized
Complexes 3a-c[Y] (Y ) PF6, TCNE, TCNQ). The hexaflu-
orophosphate salts of the Fe(III) cations were generated by
chemical oxidation of the neutral parents (3a-c), using 1 equiv
of [(C5H5)2Fe][PF6], and they were isolated as air-sensitive, but
thermally stable powders. The color of the salts depends on the
The cyclic voltammograms (CV) of all complexes display a
reversible one-electron wave (Table 2) in the range 0.02
V/-0.13 V vs SCE, which corresponds to the Fe(II)/Fe(III)
redox couple. A second irreversible process located before the
solvent edge was observed around 1.0 V. This process involves
more than one electron and could be assigned to an oxidation
involving the anthracene fragment. Indeed, in the related series
of complexes 1 a second irreversible process was observed at
more positive potentials (1.35–1.40 V) and attributed to the
Fe(III)/Fe(IV) couple. The reversible process corresponds to the

1916 Organometallics, Vol. 27, No. 8, 2008
de Montigny et al.
Table 1. IR Frequencies (cm-1) for Selected Fe(II) and Fe(III)
Table 3. 57Fe Mössbauer Fitting Parameters at 80 K for Selected
Complexes
a
Complexes in Nujol and CH2Cl2
compd
Fe(II)
(2053)
Fe(III)b
∆νC≡C
ref
compd
1a
1a[PF6]
3a
3a[PF6]
3b
3b[PF6]
3c
3c[PF6]
3c[TCNE]
3c[TCNQ]
3d
IS (mm s-1
)
QS (mm s-1
)
Γ (mm s-1
)
ref
1a
(2021)
(1988)
(2017)
not obsd
-32
-65
-37
26
0.28
0.25
2.02
0.90
na
na
26
26
1b
1c
2053 (2054)
2047 (2048)
2028
2022
2001
26
26
0.264
0.110
0.251
0.116
0.239
0.242
0.259
0.232
0.260
1.945
0.825
1.883
0.927
1.863
0.913
0.849
0.791
1.910
0.134
0.213
0.129
0.192
0.131
0.199
0.146
0.142
0.128
this work
this work
this work
this work
this work
this work
this work
this work
this work
3a
3b
3c
2018
1957
-4
-44
-10
-9
this work
this work
this work
1986 (1968)
1976 (1965)
1977 (1966, 1992)c
1951 (1967, 1992)d
-35
3d
3e
2118
1998
2111
2011
this work
this work
in Diels–Alder additions with anthracene and its analogues.49–52
In the case of complex 3c, the electron transfer is the unique
observed reaction.
a Values in CH2Cl2 are given in brackets. b With PF6 counteranion
-
unless specified. c TCNE as counteranion. d TCNQ as counteranion.
Characterization of the Fe(III) derivatives was performed by
the usual spectroscopic methods complemented for many of
them by HRMS and/or elemental analysis. As expected, these
dark compounds present a voltammogram identical with those
obtained for their neutral parents, while their spectroscopic
characteristics resemble those reported for 1a-c[PF6].26,53 For
the five complexes 3a-c[PF6], 3c[TCNE], and 3c[TCNQ], the
IR absorption corresponding to the νC≡C stretch is shifted to
lower wavenumbers relative to the respective neutral parents
(Table 1, ∆νC≡C). This shift follows the same trend that was
observed in the related series 1. In addition, for 3c[PF6], the
oxidation is evidenced by a 14 cm-1 shift of the CtN stretching
mode toward higher wavenumbers, indicating a decrease of the
retrodonation of the anthracene group in the antibonding
π*(CtN) orbital.
Some iron(II) and iron(III) complexes were also characterized
by 57Fe Mössbauer spectroscopy at 80 K. These results are
reported in Table 3 and compared to measurements already
found for 1a and 1a[PF6].26 Examination of the line width of
the Mössbauer spectra reveals that broader lines were obtained
for the compounds 3b[PF6] and 3c[PF6] (larger Γ values). The
broadness of the lines suggests that the iron nuclei can exist in
slightly different environments for these two compounds. In the
case of the complex 3c[PF6] an X-ray crystal structure was
obtained and two crystallographically different molecules were
found in the unit cell (see below). One can assume that the line
broadening probably has the same origin in the case of
compound 3b[PF6].
Scheme 3. Electronic Structures for 3 and 3+
Table 2. Electrochemical Data for Selected Complexes
a
compd
∆Ep
E0
ic/ia
ref
1a
1b
1c
3a
3b
3c
3d
3e
0.08
0.08
0.08
0.08
0.09
0.08
0.08
0.06
-0.15
-0.12
-0.05
-0.13
-0.08
0.02
1
1
1
1
1
1
1
1
26
26
26
this work
this work
this work
this work
this work
-0.10
-0.11
a All values in V vs SCE. Conditions: CH2Cl2, 0.1 M [nBu4N][PF6]
supporting electrolyte, 20 °C, Pt electrode, sweep rate 0.100 V s-1. The
ferrocene/ferrocenium couple was used as internal reference for
potentials measurements. E0 values corrected for Fc/Fc+ at 0.460 V vs
SCE in CH2Cl2.
nature of the substituents X, and varies from dark blue to black
and brown for 3a[PF6], 3b[PF6], and 3c[PF6], respectively.
Furthermore, treatment of 3c with 1 equiv of tetracyanoethylene
(TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ) at –80
°C in THF provided the complexes 3c[TCNE] and 3c[TCNQ]
which were isolated as brown (81%) and black (82%) powders,
respectively. The redox potentials of TCNE and TCNQ being
of 0.264 and 0.196 V vs SCE respectively, they were previously
used as efficient reagents for the oxidation of related electron-
rich metal complexes.43 However, it is noteworthy that electron-
deficient alkenes, such as TCNE, readily add to the CtC triple
bond adjacent to transition metals to give tetracyanocyclobute-
nyl, tetracyanobutadienyl, or allylic (vinylcarbene) complexes,
according to conditions.44–48 These alkenes can also be involved
The isomeric shift (IS) and quadrupolar splitting (QS) values
found for the neutral complexes are very close to those
previously obtained in the (η2-dppe)(η5-C5Me5)FesCtCsR
(45) Bruce, M. I.; Liddell, M. J.; Snow, M. R.; Tiekink, E. R. T.
Organometallics 1987, 7, 343.
(46) Bruce, M. I.; Hambley, T. W.; Snow, M. R.; Swincer, A. G.
Organometallics 1985, 4, 501.
(47) Bruce, M. I.; de Montigny, F.; Jevric, M.; Lapinte, C.; Skelton,
B. W.; Smith, M. E.; White, A. H. J. Organomet. Chem. 2004, 689, 2860–
2871.
(48) Bruce, M. I.; Low, P. J.; Hartl, F.; Humphrey, P. A.; de Montigny,
F.; Jevric, M.; Lapinte, C.; Perkins, G. J.; Roberts, R. L.; Skelton, B. W.;
White, A. H. Organometallics 2005, 24, 5241–5225.
(49) Atherton, J. C. C.; Jones, S. Tetrahedron 2003, 59, 9039.
(50) Bouas-Laurent, H.; Castellan, A.; Desvergne, J.-P.; Lapouyade, R.
Chem. Soc. ReV. 2001, 30, 248.
(51) Kim, J. H.; Hubig, S. M.; Linderman, S. V.; Kochi, J. K. J. Am.
Chem. Soc. 2001, 123, 87.
(43) Roger, C.; Hamon, P.; Toupet, L.; Rabaâ, H.; Saillard, J.-Y.; Hamon,
J.-R.; Lapinte, C. Organometallics 1991, 10, 1045–1054.
(44) Bruce, M. I.; Smith, M. E.; Skelton, B. W.; White, A. H. J.
Organomet. Chem. 2001, 484, 637–639.
(52) Hashimoto, M.; Yamamura, K.; Yamane, J. Tetrahedron 2001, 57,
10253.
(53) Paul, F.; Mevellec, J.-Y.; Lapinte, C. Dalton Trans. 2002, 1783–
1790.

Piano-Stool Iron Acetylides
Organometallics, Vol. 27, No. 8, 2008 1917
series.54,55 However, one can note for the Fe(II) neutral
complexes that the QS parameters are small suggesting a
significant contribution of the mesomeric form B (Scheme 3)
in the description of the electronic structure of the complexes
3. Indeed, it has been shown in these series of complexes, the
QS parameter is very sensitive to the nature of the Fe-C bond
and usually decreases with the Fe-C bond distance.55 The
parameters determined for the cationic Fe(III) compounds are
typical for 17-electron low-spin Fe(III) complexes. Probably,
the contribution of the canonical form B′ (Scheme 3) is weak
but significant in the description of the electronic structure of
Fe(III) complexes and its weight, which depends on the nature
of X, increasing in the order H < Br ≈ CN. In contrast with
our observations for the binuclear complexes 2+ and 22+ where
the anthracenyl bridge favors the carbon character of the
SOMO’s,40 in the mononuclear complexes 3 Mössbauer data
do not suggest a significant spin distribution onto the ethyny-
lanthracenyl ligand in contrast with reported results on ruthenium
homologues.56 Comparison of the previous results26 with those
obtained for the anthracene-containing series 3 indicates that
the anthracene enhances the cumulenic character and increases
the sensitivity to the electronic properties of X (Scheme 3).
3c, 3c[PF6], 3c[TCNQ], and 3c[TCNE], respectively, as shorter
metal-metal distances.
Interestingly, comparison of the Fe-P distances in 3c,
3c[PF6], 3c[TCNE], and 3c[TCNQ] reveals that the anion-cation
interaction can play a significant role on the structure of the
cation. Indeed, the Fe-P distances increase 3.8% from 3 to
3c[PF6] or 3c[TCNE] and only 1.8% to 3c[TCNQ]. It is also
noteworthy that the distances between the cation and its anion
strongly depend on the nature of the latter. In this trend, the
distances between anion and cation decrease from 11.43 Å
(TCNQcent-Fe) to 6.18/6.38 Å (PF6-Fe) and to 5.41 Å
(TCNEcent-Fe, 293 K) and even to 5.32 Å for the same salt at
100 K. The increase of the cation–anion Coulombic interaction
with the decrease of the cation–anion distance is corroborated
by the increase of the IS parameter of the Mössbauer spectra,
which reflects the increase of the electronic density at the iron
nucleus in the order TCNQ < PF6 < TCNE.
The apparent charge per TCNQ anion can be determined from
the exocyclic double bond lengths.58 They vary from 1.36 Å
for TCNQ to 1.40 Å for [TCNQ]- and 1.43 Å for [TCNQ]2- 59
.
In 3c[TCNQ], these distances (1.414(3) Å) are consistent with
a full negative charge on the TCNQ anion. Similarly, in the
case of TCNE, the central CdC bond elongates by 4% from
1.35 Å to 1.39 Å for a one-electron reduction60 and to 1.49 Å
for a two-electron reduction.61 The observed CdC bond distance
in 3c[TCNE] of 1.404(5) Å at 293 K is also fully consistent
with a full negative charge on the TCNE anion. Interestingly,
X-ray diffraction data recorded at 100 K show that the central
CdC bond length increases upon cooling (1.422(2) Å) sug-
gesting that the degree of negative charge still increases when
the temperature decreases. These results are consistent with both
the redox potentials43 and the Mössbauer QS values which are
typical for iron(III) of these series.54,55
π-π stacking is an important attribute of polyaromatic
hydrocarbons like anthracenes which can affect different proper-
ties of the materials made from these compounds.62 Thus special
attention was paid to analyze these noncovalent π-π interac-
tions in the molecular structures of these complexes. The
complexes 3b, 3c, 3c[PF6], and 3c[TCNQ] do not exhibit any
π-π stacking in the solid state. Apparently, the presence of
the bulky (η2-dppe)(η5-C5Me5)Fe moiety is sufficient to push
the anthracene rings further apart and disrupt the π-π stacking.
However, analysis of the crystal structure of 3c[TCNE] reveals
an intermolecular π-π stacking of the anthracene rings. The
anthracene planes are parallel and the plane-to-plane distance
is 3.437 Å at 100 K and slightly increases with temperature to
3.494 Å at 293 K. These values tend to be on the short side of
usual range of 3.3–3.9 Å for such interactions.63,64 The
centroid-centroid vector length between stacked aromatic rings
(4.080 Å) is longer than the plane-to-plane distance indicating
a displacement between stacked rings. This degree of displace-
Comparison of the IS and QS parameters obtained for 3c[Y]
(Y ) PF6, TCNE, TCNQ) shows the nature of the counteranion
is sensed by the iron nucleus. The distant anions which surround
the Mössbauer atom contribute to the total electric field (EFG)
and consequently the QS values depend on their volume and
symmetry.57 The IS parameters reflect the electron density at
the iron nucleus,57 and should decrease as the distance between
the iron nucleus and the anion increases. As expected, the
smallest IS value is obtained for 3c[TCNQ] for which the largest
anion-cation distance was found (see below). In the case of
the complexes 3c[PF6] and 3c[TCNE] the distances between
the iron center and the centroid of the anion are very similar,
consequently, the IS values should be very close (see below).
However, one can note that the IS parameter is larger in the
case of 3c[TCNE] indicating a stronger anion-cation interaction
in this latter case. This was confirmed by the observation of a
π-π stacking interaction between the TCNE anion and the
C5Me5 ligand as described in the next section.
4. Molecular Structures of 3b, 3c, 3c[PF6], 3c[TCNE],
and 3c[TCNQ]. Monocrystals of 3b, 3c, 3c[PF6], 3c[TCNE],
and 3c[TCNQ] were grown, and the corresponding structures
could be solved (Figure 1). The X-ray data are listed in Table
4 and the relevant bond distances and angles are given in Table
5. As invariably noted in the (η2-dppe)(η5-C5Me5)Fe series the
iron centers exhibit octahedral geometry with bond lengths and
angles in previously established ranges.4,21,26,43,55 Comparison
of the data obtained for Fe(II) and Fe(III) complexes shows the
expansion of the coordination sphere upon oxidation as invari-
ably observed for organoiron derivatives.28 This is the major
change associated with the reversible electron transfer. Only
very small geometrical differences take place in the anthracenyl
acetylide fragment when the oxidation state of the iron changes.
The intermolecular Fe(II)-Fe(II) and Fe(III)-Fe(III) arrange-
ments give 9.75, 11.01, 9.60, and 12.41 Å for the complexes
(58) Miller, J. S.; Zhang, J. H.; Reiff, W. M.; Dixon, D. A.; Preston,
L. D.; Reis, A. H.; Gebert, E.; Extine, M.; Troup, J.; Epstein, A.; Ward,
M. D. J. Am. Chem. Soc. 1987, 91, 4344–4360.
(59) Hoekstra, A.; Spoelder, T.; Vos, A. Acta Crystallogr. 1972, B28,
14–24.
(60) Miller, J. S.; Calabrese, J. C.; Rommelmann, H.; Chittipeddi, S. R.;
Zhang, J. H.; Reiff, W. M.; Epstein, A. J. J. Am. Chem. Soc. 1987, 109,
769–781.
(54) Guillaume, V.; Thominot, P.; Coat, F.; Mari, A.; Lapinte, C. J.
Organomet. Chem. 1998, 565, 75–80.
(61) Dixon, D. A.; Miller, J. R. J. Am. Chem. Soc. 1987, 109, 3656–
3664.
(55) Argouarch, G.; Thominot, P.; Paul, F.; Toupet, L.; Lapinte, C. C. R.
Chim. 2003, 6, 209–222.
(62) Goddard, R.; Haenel, M. W.; Herndon, W. C.; Kruger, C.; Zandler,
M. 1995, 117, 30.
(56) Fox, M. A.; Roberts, R. L.; Khairul, W. M.; Hartl, F.; Low, P. J.
J. Organomet. Chem. 2007, 692, 3277–3290.
(63) Ionkin, A. S.; Marshall, W. J.; Wang, Y. Organometallics 2005,
24, 619.
(57) Gütlich, P.; Link, R.; Trautwein, A. Mössbauer Spectroscopy and
Transition Metal Chemistry; Springer-Verlag: Berlin, Germany, 1978; Vol.
3, p 280.
(64) Ionkin, A. S.; Marshall, W. J.; Fish, B. M. Organometallics 2006,
25, 1461–1471.

1918 Organometallics, Vol. 27, No. 8, 2008
de Montigny et al.

Piano-Stool Iron Acetylides
Organometallics, Vol. 27, No. 8, 2008 1919
Table 5. Selected Distances (Å) and Angles (deg) for 3b, 3c, 3c[PF6], 3c[TCNE], and 3c[TCNQ]
3c[TCNE]
3b
3c · 2CH2Cl2
3c[PF6] · CH2Cl2
293 K
1.779
100 K
1.777
3c[TCNQ]
Fe(Cp*a)centroid
Fe-P1
1.749
1.757
1.777/1.772
1.770
2.181(2)
2.181(2)
1.887(5)
1.216(7)
1.442(7)
1.408(8)
1.409(9)
1.346(10)
1.366(11)
1.344(11)
1.435(10)
1.431(8)
1.393(10)
1.376(10)
1.466(8)
1.424(10)
1.414(10)
1.336(13)
1.408(13)
1.317(11)
1.424(10)
1.912(5)
2.182(1)
2.182(1)
1.879(3)
1.234(4)
1.420(4)
1.425(4)
1.428(4)
1.363(5)
1.417(5)
1.371(5)
1.422(4)
1.436(4)
1.415(4)
1.410(4)
1.431(4)
1.425(4)
1.429(4)
1.361(4)
1.414(4)
1.370(4)
1.423(4)
1.434(4)
1.144(5)
129.1
2.265(2)/2.264(2)
2.268(2)/2.266(2)
1.878(7)/1.874(6)
1.211(9)/1.227(9)
1.428(9)/1.425(9)
1.418(11)/1.429(11)
1.378(12)/1.402(12)
1.370(12)/1.394(12)
1.439(14)/1.408(14)
1.356(15)/1.340(14)
1.407(12)/1.424(12)
1.461(10)/1.422(10)
1.373(12)/1.394(12)
1.421(12)/1.410(11)
1.433(9)/1.426(9)
1.408(11)/1.402(10)
1.410(12)/1.406(12)
1.342(12)/1.370(12)
1.418(11)/1.400(11)
1.352(12)/1.348(11)
1.422(10)/1.415(10)
1.436(10)/1.438(10)
1.146(9)/1.141(9)
131.6/132.2
129.5/128.4
122.7/122.6
85.16(8)/84.73(8)
87.8(3)/87.7(2)
85.0(2)/86.7(2)
177.2(6)/178.1(6)
178.2(7)/177.7(8)
121.0(7)/120.2(6)
124.0(7)/121.6(7)
118.3(9)/119.7(8)
117.6(9)/118.8(8)
175.6(10)/177.8(10)
2.2709(7)
2.2675(7)
1.886(2)
1.217(3)
1.435(3)
1.421(4)
1.424(4)
1.351(4)
1.412(4)
1.357(5)
1.425(4)
1.425(3)
1.406(4)
1.406(4)
1.434(3)
1.417(4)
1.419(4)
1.344(4)
1.410(4)
1.357(4)
1.412(4)
1.445(3)
1.131(3)
131.5
129.7
123.6
84.2(1))
89.3(1)
83.1(1)
177.9(2)
177.4(3)
120.4(2)
122.5(2)
118.7(3)
118.8(3)
178.7(4)
2.2650(5)
2.2690(5)
1.884(2)
1.220(2)
1.427(2)
1.419(2)
1.422(2)
1.362(2)
1.414(2)
1.361(2)
1.426(2)
1.428(2)
1.408(2)
1.405(2)
1.429(2)
1.422(2)
1.423(2)
1.358(2)
1.415(2)
1.363(2)
1.422(2)
1.436(2)
1.144(2)
131.7
2.2245(7)
2.2291(7)
1.872(2)
1.223(2)
1.423(2)
1.421(3)
1.419(3)
1.355(3)
1.407(3)
1.355(3)
1.417(3)
1.431(2)
1.409(3)
1.401(3)
1.432(3)
1.425(3)
1.422(3)
1.352(4)
1.404(4)
1.362(3)
1.418(3)
1.435(3)
1.133(3)
1.329
Fe-P2
Fe-C37
C37-C38
C38-C39
C39-C40
C40-C41
C41-C42
C42-C43
C43-C44
C44-C45
C45-C40
C45-C46
C46-C47
C47-C52
C52-C39
C47-C48
C48-C49
C49-C50
C50-C51
C51-C52
C46-C53/Br
C53-N1
(Cp*)centroidFe-P1
(Cp*)centroidFe-P2
(Cp*)centroidFe-C37
P1-Fe-P2
P1-Fe-C37
P2-Fe-C37
Fe-C37-C38
C37-C38-C39
C40-C39-C52
C45-C46-C47
C45-C46-C53/Br
C47-C46-C53/Br
C46-C53-N1
132.9
130.7
120.3
133.2
120.5
129.6
123.5
130.1
121.7
83.9(3)
87.3(1)
85.58(6)
86.90(17)
84.67(17)
179.4(6)
172.3(6)
119.3(6)
123.8(5)
117.9(5)
118.2(5)
85.61(3)
85.80(9)
87.81(9)
178.8(3)
177.7(3)
118.9(3)
121.4(3)
119.5(3)
119.1(3°
179.3(4)
83.98(2)
89.72(4)
82.74(4)
177.7(2)
177.2(2)
120.3(2)
122.2(2)
118.5(2)
119.2(2)
178.7(2)
85.7(1)
177.6(2)
176.7(2)
119.7(2)
122.3(2)
118.4(2)
119.2(2)
178.6(3)
a Cp* ) (η5-C5Me5).
Table 6. ESR Dataa for Selected Fe(III) Complexes
ment between the rings can be defined by the ꢀ angle between
the ring centroid vector and the ring normal to the plane of one
aromatic ring. The value of ꢀ is 19.96° and the displacement
between the rings compares well with data determined for other
π-stacked aromatic rings.65 Using the C5Me5 ligand on each
molecule interacting in the dyad as a reference point for
analyzing the conformation about the carbon-rich ligand and
the centroid to define a torsion angle (θ), with θ ) 180° and 0°
corresponding to anti and syn arrangements, respectively, we
see that compound 3c[TCNE] shows an almost gauche arrange-
ment of the terminal ends (θ ) 80°). This geometry is close to
the conformation observed for the (η2-dppe)(η5-C5Me5)FeCt
CCtCFe(η5-C5Me5)(η2-dppe) binuclear complex, but consti-
tutes a notable difference from the analogue with a -C8- all-
carbon bridge66 or the binuclear complexes 2cn+ (n ) 0, 1, 2).40
In addition, the crystal structure reveals anion-cation interac-
tion. The C5-ring–TCNE plane has a 6.4° dihedral angle, and
the distance between the centroids of the C5Me5 ligand and
TCNE anion is 3.595 Å.
compd
g1
g2
g3
g
∆g
ref
1a[PF6]
1c[PF6]
3a[PF6]
3c[PF6]
1.975
1.970
1.978
1.973
1.976
1.978
2.033
2.028
2.037
2.027
2.032
2.027
2.464
2.499
2.412
2.496
2.483
2.485
2.157
2.166
2.195
2.234
2.164
2.163
0.489
0.529
0.434
0.523
0.507
0.507
28
28
this work
this work
this work
this work
3c[TCNE]
3c[TCNQ]
a At 77 K in CH2Cl2-C2H4Cl2 (1:1) glass.
served for d5 low-spin iron(III) in pseudooctahedral geometry.4,67
The g values extracted from the spectra are collected in Table
6, together with some g values of selected complexes of the
(η2-dppe)(η5-C5Me5)Fe series. As observed in previous ESR
investigations on similar compounds, the anisotropy tensor (∆g)
of the ESR spectra increases with the electron-withdrawing
capability of the substituents.28 One can note that this sensitivity
of the electronic properties to the substituents is larger in the
anthracene series, which confirms that anthracene fragments act
as better transmitters than phenyl rings. Note that the large
isotropic tensor, g ) 1/3(g1 + g2 + g3), and the large anisotropy
of the signal (∆g ) g3 - g1) confirm the large metallic character
of the SOMO already deduced from the Mössbauer quadrupole
splitting parameter. The spectra of 3c[TCNE] and 3c[TCNQ]
displayed an extra signal corresponding to the paramagnetic
anions observed at g ) 2.0027 and 2.0019, respectively. The
ESR spectra run with solid samples were poorly resolved.
5. ESR Spectroscopy. The X-band ESR spectra run at 77
K in a rigid glass (CH2Cl2/C2H4Cl2, 1:1) for the complexes
3a[PF6] and 3c[PF6] display three well-resolved features cor-
responding to the components of the g tensor, as usually ob-
(65) Cuffe, L.; Hudson, R. D. A.; Gallagher, J. F.; Jennings, S.;
McAdam, C. J.; Connelly, R. B. T.; Manning, A. R.; Robinson, B. H.;
Simpson, J. Organometallics 2005, 24, 2051–2060.
(66) Coat, F.; Paul, F.; Lapinte, C.; Toupet, L.; Costuas, K.; Halet, J.-
F. J. Organomet. Chem. 2003, 683, 368–378.
(67) Rieger, P. H. Coord. Chem. ReV. 1994, 135/136, 203–286.

1920 Organometallics, Vol. 27, No. 8, 2008
de Montigny et al.
Table 7. UV–Vis Absorption and Emission Spectral Data of Complexes 1–3
complex
absa λ/nm (103 ꢀ/dm3 mol-1 cm-1
)
medium (T/K) emission λ/nm (τo/µs)
Φlum
ref
1a
245 (34.0), 348 (13.6)
b
b
b
b
b
b
b
b
8
8
26
26
1a[PF6] 241(sh, 34.0), 267 (37.0), 575 (2.2), 663 (2.9)
1c
1c[PF6]
267 (sh, 17.8), 281 (sh, 16.1), 387 (sh, 10.3), 445 (16.4)
263 (sh, 40.5), 326 (sh, 12.5), 394 sh, 2.8), 458 (sh, 1.4), 501 (1.0), 652
(0.9)
2
268 (9.3), 334 (2.1), 391 (1.2), 410 (1.1), 622 (2.3)
CH2Cl2 (298)
glassc (77)
441(<0.1)
394 (0.16)
446(<0.1)
441 (0.17)
445(<0.1)
393 (0.16)
404(<0.1)
401 (0.18)
466(<0.1)
1.82 × 10-3 this work
1.68 × 10-3 this work
3.59 × 10-4 this work
3.95 × 10-3 this work
1.11 × 10-2 this work
2[PF6]
2[PF6]2
3a
267 (11.1), 400 (2.1), 450 sh (1.4), 823 (4.8), 954 sh (1.8)
265 (5.7), 408 (2.3), 468 (1.6), 818 (2.9)
260 (sh, 55.9), 372 (6.1), 553 (5.7)
CH2Cl2 (298)
glassc (77)
CH2Cl2 (298)
glassc (77)
CH2Cl2 (298)
glassc (77)
3a[PF6] 266 (sh, 52.8), 399 (sh, 8.2), 534 (sh, 5.4), 604 (sh, 6.0), 884 (0.7),
CH2Cl2 (298)
1012 (1.0), 1887 (0.1)
glassc (77)
420 (0.20)
426(<0.1)
449 (0.17)
433(<0.1)
3c
268 (sh, 71.2), 320 (14.0), 396 (sh, 6.4), 602 (sh, 14.7) 651 (sh, 16.7)
CH2Cl2 (298)
7.75 × 10-3 this work
3.74 × 10-3 this work
glassc (77)
3c[PF6]
272 (sh, 59.6), 399 (sh 9.2), 537 (sh, 9.1), 604 (sh 4.6), 441 (sh, 16.4),
896 (1.0), 1024 (1.4), 1974 (0.3)
CH2Cl2 (298)
glassc (77)
425 (0.16)
a Measured in CH2Cl2 at 293 K. b Not measured. c Measured in 2-methyltetrahydrofuran.
However, one can note the very weak intensity of the ESR signal
obtained with solid samples of 3c[TCNE] suggesting antifer-
romagnetic exchange interaction between the organometallic
cation and the organic anion as observed in the crystal structure.
6. Uv–vis–NIR Absorption Spectroscopy. The UV–vis
spectra of the neutral complexes were recorded in the range
250–900 nm. They resemble the spectra previously reported for
the related para-substituent functionalized organoiron(II) com-
pounds 1 (Table 7). Besides the high-energy transition at ca.
260-270 nm, which can apparently be attributed to π-π*
ligand-centered transitions, less intense transitions were observed
at ca. 370 nm for 3a and 320 and 400 nm for 3c. They constitute
spectroscopic signatures of the anthracene fragment. Broad
absorptions in the visible range are at the origin of the raspberry
color of 3a (553 nm) and dark blue color of 3c (602 sh, 651
nm). Similar to the phenylethynyl series, these transitions can
be assigned to MLCT transitions.26 However, in comparison
with 1a and 1c these transitions are red-shifted by ca. 200-215
nm, i.e., 7100-10500 cm-1, for both compounds showing that
9,10-anthracenyl acts as a much more efficient transmitter than
phenyl.
The UV–vis spectra of the Fe(III) complexes 3a and 3c
display several absorptions which were found for all Fe(III)
alkynyl complexes.28 In particular, two distinct peaks are
apparent in the 800–1050 nm range at the border between the
visible and near-infrared range. For the related Fe(III) complexes
of the 4-phenylethynyl series, corresponding absorptions were
observed in the 600–850 nm spectral range and attributed to
LMCT transitions.28
Measurements in the NIR range confirm the transparency of
the Fe(II) complexes while the spectra of Fe(III) counterparts
3a[PF6] and 3c[PF6] present a weak absorption in the 1500–2000
nm range. As evidenced for 1a[PF6] and 1c[PF6] this absorption
characteristic of Fe(III) complexes is reminiscent of a forbidden
metal-centered ligand field electronic transition.28
7. Luminescence Spectroscopy. Upon excitation at λ g 350
nm at room temperature, the CH2Cl2 solutions of the anthracenyl
complexes 2, 2[PF6], 2[PF6]2, 3a, 3a[PF6], 3c, and 3c[PF6] emit
in the blue region. The emission spectra of these complexes
are dominated by high-energy emission bands at ca. 404-472
nm and some of them with vibronic structures. For the
mononuclear complexes 3a, 3a[PF6], 3c, and 3c[PF6], in general,
the cyano-substituted complexes (i.e., 3c and 3c[PF6]) emit at
Figure 2. Normalized emission spectra of 3a, 3c, and 3c[PF6] in
degassed dichloromethane at room temperature.
lower energies relative to their corresponding unsubstituted
counterparts (i.e., 3a and 3a[PF6]). In addition, the Fe(III)
complexes (i.e., 3a[PF6] and 3c[PF6]) show slight red shifts in
emission energies relative to the Fe(II) counterparts (i.e., 3a
and 3c) as shown in Figure 2. These observations are probably
the results of the electron-withdrawing properties of the cyano
and the Fe(III) groups on the anthracenyl moieties. Similar
findings were also observed in the low-temperature glass state
emission spectra. The dinuclear complexes 2, 2[PF6], and
2[PF6]2 were found to emit at nearly identical wavelengths and
band shapes both in room temperature solution state and low-
temperature glass state, indicating that the [Fe(dppe)Cp*]
moieties have little influence on the emission energies of this
class of anthracenyl alkynyl complexes. Since emission bands
with similar vibronic structures and energies were observed in
the corresponding free ligands, the highly structured emission
bands of these anthracenyl alkynyl complexes with lifetime <0.1
µs at room temperature were tentatively assigned as the ligand-
centered emission of the alkynyl anthracene units. The lumi-
nescence quantum yields of these anthracenyl complexes are
much lower than that of anthracene (Φem ≈ 0.3) and are nearly
independent of the oxidation states of the iron moieties. Such a
reduction in luminescence quantum yield in the anthracenyl
complexes could be rationalized by the introduction of low-
lying nonemissive excited states upon incorporation of the
transition metal moieties which quenched the emission. Reduc-

Piano-Stool Iron Acetylides
Organometallics, Vol. 27, No. 8, 2008 1921
ments were performed on a multinuclear Bruker WB 300 instru-
ment. Chemical shifts are given in parts per million relative to
tetramethylsilane (TMS) for 1H and 13C NMR spectra, and H3PO4
for 31P NMR spectra. X-Band ESR spectra were recorded on a
Bruker ESP-300E spectrometer. An Air Products LTD-3-110 liquid
helium transfer system was attached for the low-temperature
measurements. Transmittance FTIR spectra were recorded with a
Bruker IFS128 spectrometer (400–7500 cm-1). Liquid near-infrared
spectra were recorded on a Cary 5 spectrometer. UV–visible spectra
were recorded on an UVIKON XL spectrometer. The 57Fe
Mössbauer spectra were obtained by using a constant acceleration
spectrometer previously described with a 50 mCi 57Co source in a
Rh matrix. The sample temperature was controlled by a Oxford
MD306 cryostat and an Oxford ITC4 temperature controller.
Computer fitting of the Mössbauer data to Lorenzian line shapes
were carried out with a previously reported computer program. The
isomer shift values are reported with respect to iron foil at 298 K
and are not corrected for the temperature-dependent second-order
Doppler shift. The Mössbauer sample cell consists of a 2 cm
diameter cylindrical plexiglass holder. Steady state excitation and
emission spectra were obtained on a Spex Fluorolog 111 spectrof-
luorometer. Elemental analyses were performed at the CRMPO,
University of Rennes 1, France.
tive electron transfer quenching is also favorable in these Fe(II)
complexes. From the electrochemical data, the Fe(II) moieties
of complexes 3a and 3c can be readily oxidized to Fe(III) at
-0.13 and +0.02 V vs SCE, respectively. With the structurally
related compound dicyanoanthracene having an excited state
reduction potential E°(An*/An-•) of about +2.00 V vs SCE,68
positive values of ∆E° for the reductive quenching process by
the Fe(II) moieties were obtained, indicating that, from a
thermodynamic point of view, intramolecular reductive electron
transfer quenching is a possible quenching mechanism for these
anthracenyl iron(II) complexes. On the other hand, the presence
of low-lying LMCT states in the Fe(III) alkynyl moieties, as
reflected by the presence of the low-energy NIR absorptions,
is capable of quenching the anthracene unit via an energy
transfer pathway. Thus the luminescence quantum yields of both
the Fe(II) and Fe(III) complexes are low and are rather
insensitive toward the oxidation state of the Fe center, which is
in contrast to our previous work on the mixed-metal complexes
of iron and rhenium,8 in which the luminescence quantum yield
of the low-energy MLCT emission of the complex is dependent
on the oxidation state of the iron moiety. The relatively high-
energy anthracene 1IL emissions observed in these anthracenyl
iron alkynyl complexes could probably be quenched by both
Fe(II) and Fe(III) moieties and that accounts for the relatively
low luminescence quantum yield of all the complexes in this
study.
(η2-dppe)(η5-C5Me5)FeCtC-ant-H (3a). A mixture of (η2-
dppe)(η5-C5Me5)FesCtCsH 8 (0.27 g, 0.44 mmol), 9-iodoan-
thracene 9 (134 mg, 0.44 mmol), PdCl2(PPh3)2 (31 mg, 0.044
mmol), and CuI (17 mg, 0.089 mmol) in THF (20 mL) and HNi-
Pr2 (20 mL) was stirred at 70 °C for 12 h to give a raspberry
solution. After evaporation to dryness, the crude product was
dissolved in toluene and passed through a short pad of neutral
alumina oxide under argon. Removal of the solvents gave a solid
that was washed twice with pentane to afford pure complex 3a as
a raspberry powder. Yield: 0.25 g (71%). Anal. Calcd for
C52H48FeP2: C, 78.98; H, 6.12. Found: C, 78.12; H, 6.07. FT-IR
(Nujol, cm-1): 2022 (νC≡C). UV–vis (CH2Cl2): λmax (ꢀ) 553 (5708),
391 (5682), 371 (5944), 260 (55863). 1H NMR (200 MHz, C6D6):
δ 8.35 (d, 2 H, Ant, J ) 8 Hz), 7.96–7.84 (m, 7 H, Ant and Ph),
7.33–6.98 (m, 20 H, Ant and Ph), 2.95 (m, 2 H, CH2), 1.92 (m, 2
H, CH2), 1.63 (s, 15 H, Cp*). 31P NMR (81 MHz, C6D6): δ 101.8
Conclusion
We have reported here the synthesis, isolation, and charac-
terization of several neutral and radical cation complexes of
the formula [(η2-dppe)(η5-C5Me5)Fe(-CtC-9,10-ant-X)]n+n[Y]
(ant ) anthracene; n ) 0, 1; 3anY, X ) H; 3bnY, X ) Br;
3cnY, X ) CN; 3d, X ) CtCsSiiPr3; 3e, X ) CtCsH; Y )
PF6-, TCNE-, TCNQ-). An extensive analysis of the properties
of this new family of molecules including redox potentials,
X-ray determination, and Mössbauer, ESR, vibrational, and
electronic spectroscopies was achieved. Comparison of these
data with those previously obtained for the mononuclear
complexes [(η2-dppe)(η5-C5Me5)Fe(CtCsC6H4X)]n+n[Y]26
clearly indicates that the anthracene enhances the cumulenic
character of the bonding and increases the sensitivity to the
electronic properties of the remote substituent X. As a result,
the 9,10-anthracenyl bridge acts as a much more efficient
transmitter than phenyl. Mössbauer and ESR data do not suggest
a significant spin distribution onto the ethynylanthracenyl ligand,
but a strong metal character for these radicals.
Despite the bulkiness of the iron building block that pushes
the anthracene rings further apart, it was shown that these forces
can be counter balanced by cation–anion interactions. Indeed,
analysis of the crystal structure of 3c[TCNE] reveals an
intermolecular π-π stacking between the anthracenes rings.
These Fe(II) and Fe(III) complexes exhibit weaker lumines-
cence property than the free carbon-rich ligand. It was shown
that both Fe(II) and Fe(III) moieties can quench the ligand-
centered emission by two different pathways.
n
(s, dppe). CV (CH2Cl2, 20 °C, 0.1 M Bu4NPF6, V ) 0.1 V/s): E°
) -0.135 V (∆Ep ) 0.069 V, ic/ia ) 1.0). High-resolution MS
(FAB) m/z 790.2580 (calcd for C52H4856FeP2 790.2581).
(η2-dppe)(η5-C5Me5)FeCtC-ant-Br (3b). [(η2-dppe)(η5-C5-
Me5)FeCtC-ant-Br][PF6] (3b[PF6], 740 mg, 0.73 mmol) and
tBuOK (90 mg, 0.80 mmol) in THF (50 mL) were stirred for 5 h
at room temperature. After evaporation to dryness, the crude product
was dissolved in ether and passed through a short pad of celite
under argon. The solid was dried under vacuum to give pure
complex 3b as a dark red powder. Yield: 0.560 g (87%). FT-IR
(Nujol, cm-1): 2011 (νC≡C). CV (CH2Cl2, 20 °C, 0.1 M nBu4NPF6,
V ) 0.1 V/s): E° ) -0.083 V (∆Ep ) 0.090 V, ic/ia ) 1.0). UV–vis
(CH2Cl2): λmax (ꢀ) 592 (6621), 392 (4830), 266 (53250). 1H NMR
(200 MHz, C6D6): δ 8.79 (d, 2 H, Ant, J ) 9 Hz), 8.44 (d, 2 H,
Ant, J ) 9 Hz), 8.03–7.93 (m, 5 H, Ph), 7.45–7.01 (m, 19 H, Ant
and Ph), 2.96 (m, 2 H, CH2), 2.02 (m, 2 H, CH2), 1.69 (s, 15 H,
Cp*). 31P NMR (81 MHz, C6D6): δ 101.2 (s, dppe). High-resolution
MS (FAB) m/z 868.1716 (calcd for C52H4756FeBrP2 868.1686).
X-ray-quality crystals of (η2-dppe)(η5-C5Me5)FeCtC-9,10-ant-Br
were grown by slow evaporation of a pentane solution of the above
compound.
Experimental Section
(η2-dppe)(η5-C5Me5)FeCtC-ant-CtN (3c). A mixture of (η2-
dppe)(η5-C5Me5)FeCtCH 8 (0.50 g, 0.81 mmol), 9-bromo-10-
cyanoanthracene 5c (0.23 g, 0.81 mmol), PdCl2(PPh3)2 (57 mg,
0.081 mmol), and CuI (31 mg, 0.163 mmol) in THF (30 mL) and
HNiPr2 (20 mL) was stirred at room temperature for 12 h to give
a deep blue solution. After evaporation to dryness, the crude product
was dissolved in toluene and passed through a short pad of neutral
General Data. All the manipulations were carried out under an
argon atmosphere with Schlenk techniques or in a Jacomex 532
drybox filled with argon. Routine NMR spectra were recorded with
a Bruker DPX 200 spectrometer. High-field NMR spectral experi-
(68) Ci, X.; Whitten, D. G. J. Phys. Chem. 1991, 95, 1988–1993.

1922 Organometallics, Vol. 27, No. 8, 2008
de Montigny et al.
alumina oxide under argon. Removal of the solvents gave a solid
that was washed twice with pentane to afford pure complex 3c as
[(η2-dppe)(η5-C5Me5)FeCtC-ant-Br][PF6] (3b[PF6]). Method
A: A mixture of (η2-dppe)(η5-C5Me5)FeCtCH 8 (980 mg, 1.61
mmol), 9,10-dibromoanthracene 5b (590 mg, 1.76 mmol),
PdCl2(PPh3)2 (112 mg, 0.16 mmol), CuI (61 mg, 0.32 mmol), and
HNiPr2 (50 mL) was stirred at 50 °C for 2 days. After evaporation
to dryness, the crude product was dissolved in ether and passed
through a short pad of celite under argon. After evaporation to
dryness, [FeCp2][PF6] (260 mg, 0.80 mmol) in THF (30 mL) was
added. Then the mixture was stirred for 3 h at –80 °C. After
evaporation of the solvents, the residue was dissolved in CH2Cl2
and precipitated by addition of Et2O. After a second partial
precipitation with CH2Cl2 and Et2O, the solid was dried under
vacuum to give pure complex 3b[PF6] as a black powder. Yield:
0.742 g (45%). Method B: In a Schlenk tube wrapped with
aluminum foil, 10-bromo-9-trimethylsilylethynylanthracene 4b (350
mg, 0.99 mmol) in 50 mL of methanol were stirred for 6 h in the
presence of 1.1 equiv of potassium carbonate (150 mg, 1.09 mmol).
Then 1.1 equiv of (η2-dppe)(η5-C5Me5)FeCl 6 (681 mg, 1.09 mmol)
and 1.1 equiv of NaBPh4 (373 mg, 1.09 mmol) were added. After
a
blue powder. Yield: 0.55 g (83%). Anal. Calcd for
C53H47FeNP2 · CH2Cl2: C, 72.01; H, 5.48. Found: C, 71.00; H, 5.38.
FT-IR (Nujol, cm-1): 2194 (νC≡N), 1986 (νC≡C). UV–vis (CH2Cl2):
λmax (ꢀ) 651 (16684), 411 (6351), 391 (6439), 320 (13951), 268
1
(71216). H NMR (200 MHz, C6D6): δ 8.55 (d, 2 H, Ant, J ) 8
Hz), 8.21 (d, 2 H, Ant, J ) 8 Hz), 7.80 (m, 4 H, Ph), 7.29–6.87
(m, 20 H, Ant and Ph), 2.78 (m, 2 H, CH2), 1.92 (m, 2 H, CH2),
1.55 (s, 15 H, Cp*). 31P NMR (81 MHz, C6D6): δ 100.8 (s, dppe).
CV (CH2Cl2, 20 °C, 0.1 M nBu4NPF6, V ) 0.1 V/s): E° ) 0.016 V
(∆Ep ) 0.086 V, ic/ia ) 1.0). High-resolution MS (FAB) m/z
815.2534 (calcd for C53H4756FeNP2 815.2533). X-ray-quality
crystals of (η2-dppe)(η5-C5Me5)FeCtC-9,10-Ant-CtN · CH2Cl2
were grown by slow diffusion of pentane into a saturated CH2Cl2
solution of the above compound.
(η2-dppe)(η5-C5Me5)FeCtC-ant-CtCSiiPr3 (3d). In a Schlenk
tube wrapped with aluminum foil, 9-triisopropylsilylethynyl-10-
ethynylanthracene obtained from 4d (300 mg, 0.77 mmol) in 50
mL of methanol and 20 mL of THF were stirred in the presence of
1.1 equiv of (η2-dppe)(η5-C5Me5)FeCl (6, 0.57 g, 0.92 mmol) and
1.1 equiv of NaBPh4 (315 mg, 0.92 mmol). After approximately
16 h of stirring, tBuOK (96 mg, 1.1 equiv) was introduced. Stirring
was maintained for 4 h before the solvent was removed. The residue
was extracted with toluene (3 × 30 mL) and passed through a short
pad of neutral aluminum oxide under argon to afford pure complex
3d as a dark red powder. Yield: 0.43 g (57%). FT-IR (Nujol, cm-1):
2118 and 1998 (s and w, νC≡C). CV (CH2Cl2, 20 °C, 0.1 M
nBu4NPF6, V ) 0.1 V/s): E0 ) –0.097 V (∆Ep ) 0.080 V; ic/ia )
1.0). UV–vis (CH2Cl2): λmax (ꢀ) 613 (2610), 423 (2850), 400 (3040),
256 (37330). 1H NMR (200 MHz, C6D6): δ 9.02 (d, 2 H, Ant, J )
8 Hz), 8.32 (d, 2 H, Ant, J ) 8 Hz), 7.45–7.30 (m, 4 H, Ph),
7.25–6.90 (m, 20 H, Ant and Ph), 2,88 (m, 2 H, CH2), 1.96 (m, 2
H, CH2), 1,61 (s, 15 H, C5(CH3)5), 1,34 (s, 21 H, SiiPr3). 31P NMR
(81 MHz, C6D6): δ 101,4 (s, dppe). High-resolution MS (FAB)
m/z 970.3915 (calcd for [C63H68SiP256Fe]+ 970.3918).
t
approximately 16 h of stirring, BuOK (122 mg, 1,1 equiv) was
introduced. Stirring was maintained for 4 h before the solvent
was removed. After evaporation to dryness, the crude product was
dissolved in ether and passed through a short pad of celite under
argon. After evaporation to dryness, [FeCp2][PF6] (230 mg, 0.70
mmol) in THF (30 mL) was added. Then the mixture was stirred
for 3 h at –80 °C. After evaporation of the solvents, the residue
was dissolved in CH2Cl2 and precipitated by addition of Et2O. After
a second partial precipitation with CH2Cl2 and Et2O, the solid was
dried under vacuum to give pure complex 3b[PF6] as a black
powder. Yield: 0.370 g (43%). FT-IR (Nujol, cm-1): 1957 (νC≡C),;
n
837 (νP-F). CV (CH2Cl2, 20 °C, 0.1 M Bu4NPF6, V ) 0.1 V/s):
E° ) -0.083 V (∆Ep ) 0.090 V, ic/ia ) 1.0). UV–vis (CH2Cl2):
λmax (ꢀ) 579 (2511), 432 (9111), 408 (8513), 271 (63080).
Mössbauer (mm/s vs Fe, 80 K): IS 0.116, QS 0.927. High-resolution
MS (FAB) m/z 868.1704 (calcd for C52H4756FeBrP2 868.1686).
[(η2-dppe)(η5-C5Me5)FeCtC-ant-CtN][PF6] (3c[PF6]). Com-
plex (η2-dppe)(η5-C5Me5)FeCtC-9,10-ant-CtN 3c (200 mg, 0.245
mmol) and [FeCp2][PF6] (77 mg, 0.233 mmol) in THF (30 mL)
were stirred for 3 h at -80 °C. After evaporation of the solvents,
the residue was dissolved in CH2Cl2 and precipitated by addition
of Et2O. After a second partial precipitation with CH2Cl2 and Et2O,
the solid was dried under vacuum to give pure complex 3c[PF6] as
a brown powder. Yield: 0.194 g (87%). FT-IR (Nujol, cm-1): 2207
(η2-dppe)(η5-C5Me5)FeCtC-ant-CtCH (3e). In a Schlenk
tube wrapped with aluminum foil, (η2-dppe)(η5-C5Me5)FesCtC-
ant-CtCsSiiPr3 3d (300 mg, 0.31 mmol) in 60 mL of THF was
stirred in the presence of 0.3 equiv of TBAF (0.09 mL g, 0.09
mmol) for 16 h at 50 °C before the solvent was removed. The
residue was extracted with ether (4 × 50 mL) and passed through
a short pad of silica under argon to afford complex 3e as a dark
red powder. Yield: 208 mg (82%). FT-IR (Nujol, cm-1): 3304 (m,
(νC≡N), 1976 (νC≡C), 833 (νP-F). NIR (CH2Cl2, cm-1): (ꢀ, ∆V1/2
)
11160 (1040, 1000), 9765 (1360, 325), 5065 (270, 350). UV–vis
(CH2Cl2): λmax (ꢀ) 537 (9100), 441 (16400), 272 (59600), 232
(34900). CV (CH2Cl2, 20 °C, 0.1 M n-Bu4NPF6, V ) 0.1 V/s): E°
) 0.027 V (∆Ep ) 0.078 V, ic/ia ) 1.0). X-ray-quality crystals of
[(η2-dppe)(η5-C5Me5)FeCtC-9,10-ant-CtN][PF6] were grown by
slow diffusion of pentane into a saturated CH2Cl2 solution of the
above compound.
ν
≡C-H), 2111 and 2011 (s and w, νj C≡C). CV (CH2Cl2, 20 °C, 0.1
n
M Bu4NPF6, V ) 0.1 V/s): E0 ) –0.112 V (∆Ep ) 0.050 V; ic/ia
1
) 1.0). H NMR (200 MHz, C6D6): δ 8.75 (d, 2 H, Ant, J ) 8
Hz), 8.15 (d, 2 H, Ant, J ) 8 Hz), 8.00–7.75 (m, 4 H, Ph), 7.25–6.90
(m, 20 H, Ant and Ph), 3.73 (s, 1 H, CtCsH), 3.00 (m, 2 H,
CH2), 2,05 (m, 2 H, CH2), 1.68 (s, 15 H, C5(CH3)5). 31P NMR (81
MHz, C6D6): δ 101,8 (s, dppe).
[(η2-dppe)(η5-C5Me5)FeCtC-ant-H][PF6] (3a[PF6]). Complex
(η2-dppe)(η5-C5Me5)FeCtC-9-ant-H 3a (200 mg , 0.253 mmol)
and [FeCp2][PF6] (79 mg, 0.240 mmol) in THF (30 mL) were stirred
for 2 h at -80 °C. After evaporation of the solvents, the residue
was dissolved in CH2Cl2 and precipitated by addition of Et2O. After
a second partial precipitation with CH2Cl2 and Et2O, the solid was
dried under vacuum to give pure complex 3a[PF6] as a dark blue
powder. Yield: 0.191 g (85%). FT-IR (Nujol, cm-1): 2018 (νC≡C),
837 (νP-F). NIR (CH2Cl2, cm-1): (ꢀ, ∆V1/2) 11310 (700, 1000), 9880
(1030, 300), 5300 (100, 375). UV–vis (CH2Cl2): λmax (ꢀ) 604 (6000),
534 (5400), 418 (6800), 396 (8200), 373 (7600), 266 (52800), 259
[(η2-dppe)(η5-C5Me5)FeCtC-ant-CtN][TCNE] (3c[TCNE]).
Complex (η2-dppe)(η5-C5Me5)FeCtC-9,10-ant-CtN 3c (150 mg,
0.184 mmol) and 23.5 mg of TCNE (0.184 mmol) in THF (20 mL)
were stirred for 2 h at –80 °C. After evaporation of the solvents,
the residue was dissolved in CH2Cl2 and precipitated by addition
of Et2O. After filtration, the solid material was washed with Et2O
and dried under vacuum to give pure complex 3c[TCNE] as a brown
powder. Yield: 0.14 g (81%). Anal. Calcd for C59H47FeN5P2: C,
75.08; H, 5.02. Found: C, 74.80; H, 4.98. FT-IR (Nujol, cm-1):
2217 (νC≡N), 2183 (νC≡N), 2144 (νC≡N), 1977 (νC≡C). NIR (CH2Cl2,
cm-1): (ꢀ, ∆V1/2) 11210 (920, 1000), 9765 (1270, 325), 5060 (250,
400). UV–vis (CH2Cl2): λmax (ꢀ) 538 (8600), 439 (21400), 273
n
(52500), 231 (48100). CV (CH2Cl2, 20 °C, 0.1 M Bu4NPF6, V )
n
0.1 V/s): E° ) -0.134 V (∆Ep ) 0.080 V, ic/ia ) 1.0). ESR
(CH2Cl2/C2H4Cl2 1/1, 77 K): gx ) 2.412; gy ) 2.037; gz ) 1.978.
High-resolution MS (FAB) m/z 790.2559 (calcd for [C52H4856FeP2]+
790.2581).
(61900), 234 (42800). CV (CH2Cl2, 20 °C, 0.1 M Bu4NPF6, V )
0.1 V/s): E°1 ) 0.263 V (∆Ep ) 0.074 V, ic/ia ) 1.0); E°2 ) 0.017
a
c
V (∆Ep ) 0.070 V, Ip /Ip ) 1.0); E°3 ) –0.758 V (∆Ep ) 0.108
V,Ipa/Ipc)1.0).X-ray-qualitycrystalsof[(η2-dppe)(η5-C5Me5)FeCtC-

Piano-Stool Iron Acetylides
Organometallics, Vol. 27, No. 8, 2008 1923
a
9,10-ant-CtN][TCNE] were grown by slow diffusion of pentane
into a saturated CH2Cl2 solution of the above compound.
V (∆Ep ) 0.085 V, Ip /Ipc ) 1.0); E°2 ) 0.020 V (∆Ep ) 0.090 V,
Ip /Ipc ) 1.0); E°3 ) –0.368 V (∆Ep ) 0.075 V, ic/ia ) 1.0). X-ray-
a
[(η2-dppe)(η5-C5Me5)FeCtC-ant-CtN][TCNQ] (3c[TCNQ]).
Complex (η5-C5Me5)(dppe)FeCtC-9,10-ant-CtN 3c (200 mg,
0.245 mmol) and 50 mg of TCNQ (0.245 mmol) in THF (20 mL)
were stirred for 2 h at –80 °C. After evaporation of the solvents,
the residue was dissolved in CH2Cl2 and the temperature was
decreased to –80 °C to allow the precipitation of the product by
addition of Et2O. After a second partial precipitation with CH2Cl2
and Et2O at low temperature, the solid was dried under vacuum to
give pure complex 3c[TCNQ] as a black powder. Yield: 0.205 g
(82%). FT-IR (Nujol, cm-1): 2212 (νC≡N), 2178 (νC≡N), 2151
(νC≡N), 1951 (νC≡C). NIR (CH2Cl2, cm-1): (ꢀ, ∆V1/2) 9765 (1135,
325), 5065 (215, 400). UV–vis (CH2Cl2): λmax (ꢀ) 851 (29300),
831 (20000), 768 (14200), 750 (17400), 733 (12500), 542 (8400),
435 (24200), 421 (29700), 404 (40100), 273 (65600), 235 (38400).
quality crystals of [(η2-dppe)(η5-C5Me5)FeCtC-9,10-ant-CtN]-
[TCNQ] were grown by slow diffusion of pentane into a saturated
THF solution of the above compound.
Acknowledgment. We acknowledge the award of a grant
by CNRS/RGC under the PROCORE: France-Hong Kong
Joint Research Scheme (Project No. 09281 QE). F.d.M.
acknowledges the Ministry of Research and Education for a
fellowship.
Supporting Information Available: CIF files for 3b, 3c,
3c[PF6], 3c[TCNE], and 3c[TCNQ]. This material is available free
of charge via the Internet at http://pubs.acs.org.
n
CV (CH2Cl2, 20 °C, 0.1 M Bu4NPF6, V ) 0.1 V/s): E°1 ) 0.207
OM701278E